1. Field of the Invention
The present invention relates generally to a fuel transporting hose that is suitably used in a fuel pipe system of an automobile for transporting a liquid such as gasoline or a gas. The invention is also concerned with a resin tube incorporated in the hose, which tube has a laminar structure that consists of a layer made of fluorine-contained resin or fluororesin, and a layer made of polyamide or other resin that has a poor adhesive property with respect to the fluorine-contained resin.
2. Discussion of the Related Art
There are known various kinds of hoses made of various materials, for use in a fuel pipe system of an automobile or other vehicle. Such hoses may be used as a fuel pipe itself or as a connector for connecting fuel pipes. For example, there is known a hose (A) which consists of: an innermost layer made of fluororubber (FKM); an intermediate layer formed on the innermost layer and made of a rubber material, such as a copolymer of epichlorohydrin-ethylene oxide-allylglycidyl ether (ECO), acrylonitrile-butadiene rubber (NBR), and chlorosulphonated polyethylene (CSM); an outermost layer formed on the intermediate layer and made of ECO or CSM; and a reinforcing layer formed between the intermediate layer and the outermost layer, by braided reinforcing fibers.
There has been also proposed a hose (B) adapted for transporting town gas or other gas, as disclosed in JP-A-62-171581, which includes: an innermost layer made of a fluorine-contained resin; an intermediate layer formed on the innermost layer and made of a rubber material; and an outermost layer formed on the intermediate layer and made of a rubber material such as ethylene-propylene-diene rubber (EPDM). The hose of this type receives a considerably high pressure during its use, when used for transporting a liquefied natural gas, for example. To improve the pressure resistance, therefore, the hose further includes a reinforcing layer consisting of a brass-plated wire and formed between the intermediate layer and the outermost layer.
The above-described hose (A) has excellent properties required for its use in a fuel pipe system of an automobile, which properties include the resistance to sour gasoline which contains peroxides produced upon oxidization of gasoline at a high temperature, and the ability to prevent permeation of gasoline therethrough, in other words, gasoline impermeability. In producing the hose (A), however, each layer of the hose needs to be formed with a sufficiently large thickness, which requires a large amount of expensive fluororubber to be used for the innermost layer, resulting in an increased cost of manufacture of the hose. Further, the process of producing the hose (A) includes a series of cumbersome steps, e.g., extrusion-braiding-extrusion-vulcanization. If the above-described hose (B) is used in a fuel pipe system of an automobile, on the other hand, the hose, which has an increased heat transfer coefficient due to the reinforcing layer in the form of a metallic wire, may catch fire, and the heat generated by the fire may be transmitted to gasoline passing through the hose, thereby causing firing and explosion, and other problems.
Other than the rubber hoses as described above, a metallic tube, a resin tube or the like has been also used as a fuel pipe of an automobile or a connector for such fuel pipes. However, the metallic tube suffers from rusting, and is considerably heavy in weight, which is incompatible with the recent requirement for lightweight vehicles. In recent years, therefore, resin tubes, such as those made of polyamide or polyester resin, are widely and increasingly used in automobiles, since such tubes are lightweight and free from rusting.
For example, there is known a fuel transporting hose which consists of a single layer made of a polyamide resin.
However, the hose consisting solely of a polyamide resin layer has unsatisfactory resistance to sour gasoline, gasoline impermeability, resistance to wear due to its contact with other hoses upon installation thereof (hereinafter referred to as "wear resistance"), and resistance to shocks such as that caused by stones hit by the automobile during its running (hereinafter referred to as "shock resistance"). Further, the inner wall of the hose of this type tends to be electrically charged, due to static electricity caused by friction between the inner wall and a fuel liquid such as gasoline. If a voltage higher than a given level appears across the hose, sparks may take place between the hose and metallic parts of a vehicle body, for example, and the sparks may form holes through the hose, or may cause the fuel to take fire. Thus, the known hose is also unsatisfactory in the resistance to firing.
As described above, the single-layer tube made of a polyamide resin is undesirably highly permeable to gasoline, causing problems of environmental contamination. It is accordingly proposed to provide a tube having a double-layered structure which consists of an outer layer formed of polyamide or other resin, and an inner layer formed of fluorine-contained resin which is highly resistant to gasoline, to thereby reduce the amount of permeation of gasoline through the tube. However, the tube of this type may suffer from peeling of the inner and outer layers during its use, due to poor adhesive strength between the fluorine-contained resin and polyamide or other resin. Consequently, the tube may be closed or choked, or may burst due to a gas that is accumulated or trapped between the inner and outer layers.
To improve the adhesive strength between the inner and outer resin layers of the tube, it is known to effect a suitable surface treatment on the outer surface of the fluorine-contained resin layer which contacts the outer layer made of polyamide or other resin. As specific examples of the adhesive surface treatment, there are known various methods such as: sodium treatment using a chemical treatment liquid for introducing an active group (substituent) into the surface of the fluorine-contained resin layer; flame treatment using a flame for fusing the surface of the fluorine-contained resin layer; corona discharge method; and sputtering. However, these adhesive surface treatments have been found unsatisfactory to ensure a sufficiently high adhesive strength between the inner and outer resin layers.
It is also known to carry out a primer treatment after the adhesive surface treatment as described above, so as to improve the adhesive strength. In this case, however, the manufacturing process is undesirably complicated, and the cost of manufacturing of the resin tube is considerably increased due to an increased cost required for materials and installation associated with the primer treatment.